Conciseness

The body is dense and imperative with no concept tutorials, e.g. "Verify every `VerificationResult` before granting access" and "Never use `unsafePayloadValue` to unlock content". Minor redundancy — the Contents TOC and a Review Checklist that restates the core invariants and common mistakes — keeps it at anchor 4 (efficient with trims available) rather than anchor 5's every-token-earns-its-place.

Actionability

Concrete guidance throughout: a complete executable `PurchaseResult` switch, exact APIs (`Transaction.updates`, `AppStore.sync()`, `purchase(confirmIn:options:)`), exact states (`.pending`, `.userCancelled`, `.subscribed`, `.inGracePeriod`), and a product-type entitlement table. It sits at anchor 4 rather than 5 because a few common code paths (listener setup, entitlement-set rebuild) are described but only implemented in the reference files.

Workflow Clarity

The 7-step Implementation workflow is clearly sequenced with explicit validation checkpoints ("Test with a StoreKit configuration... and realistic renewal/refund/revocation/Ask to Buy states"; "Verify the built paywall... with real localized product data before release"), a 14-item Review Checklist, and an error-pattern-to-fix mapping in Correction reviews. This matches anchor 5 (explicit validation steps, error recovery, checklist) rather than anchor 4's minor validation gaps.

Progressive Disclosure

"Route by task" explicitly signals which of the eight existing one-level-deep reference files to load per task and when not to load them ("Do not load offer, compliance, or subscription material for a narrow consumable/non-consumable task"). The 22KB recipe file stays out of the body, matching anchor 5's clear overview with well-signaled references.

Specificity

The description lists multiple concrete actions ("Implement or review", "entitlement verification", "billing recovery", "Route physical-goods checkout to passkit") with comprehensive coverage of the domain via a ten-item list (paywalls, transactions, offers, renewal state, testing, Family Sharing, Ask to Buy, refunds). It matches the anchor for comprehensive specific actions rather than anchor 4, since no meaningful capability gaps remain.

Completeness

The "what" is explicit ("Implement or review in-app purchases and subscriptions with StoreKit 2, including...") but there is no "Use when..." clause; "Route physical-goods checkout to passkit" is boundary guidance that only weakly implies when to use the skill. Per the judging guideline a missing explicit trigger clause caps completeness at 3, and anchor 4 requires an actual, if imperfect, "when" statement.

Trigger Term Quality

Natural terms iOS developers would say are present ("in-app purchases", "subscriptions", "paywalls", "refunds", "Family Sharing", "Ask to Buy", "renewal"), but common synonyms such as "IAP" and "App Store" are absent. Good keyword coverage with a few natural terms missing fits anchor 4 rather than anchor 5's synonym-and-extension comprehensiveness.

Distinctiveness Conflict Risk

"StoreKit 2" plus "in-app purchases and subscriptions" carves out a clear niche, and "Route physical-goods checkout to passkit" actively disambiguates the nearest neighbor skill. This matches anchor 5 (clear niche with distinct triggers, minimal conflict risk) rather than anchor 4, which presumes residual overlap with closely related skills.